to that of a ported cabinet, the system low-frequency roll-off will be slightly steeper (5th-order rather than 4th-order), due to a notch (dip) in the frequency response caused by the Vap (compliance or stiffness) of the passive radiator. This notch occurs at the PR's free-air resonant frequency and causes slightly poorer transient response. Despite this, perhaps due to the lack of vent turbulence and vent pipe resonances, some listeners prefer the sound of PRs to reflex ports. PR speakers are only slightly more complex to design and are generally more expensive as compared to standard bass reflex enclosures. Applications Passive radiators are used in Bluetooth speakers, home stereo speakers, subwoofer cabinets and car audio speaker systems, particularly in cases where there is not enough space for a port or vent system. While most studio monitor speakers are either ported bass reflex designs, or closed-back without a vent or passive radiator, Mackie's HR824 and HR624 monitor speakers have a passive radiator installed on the rear of the cabinet. Focal also sells a studio monitor with a passive radiator called the SM9. Respective examples of a smart speaker and a portable Bluetooth Speaker utilizing passive radiators are Apple's HomePod mini and Ultimate Ears' UE Boom. See also Loudspeaker enclosure Bass reflex - a type of loudspeaker enclosure that uses a port (hole) or vent cut into the cabinet and a section of tubing or pipe affixed to the port Acoustic suspension - a method of loudspeaker cabinet design and utilisation that uses one or more loudspeaker drivers mounted in a sealed box or cabinet References Loudspeaker technology Audio engineering